Balloon catheters have been used for many years in a wide range of medical catheterization procedures. Two common balloon catheters designs are angioplasty dilatation balloon catheters and drug delivery balloon catheters. Both of these balloon catheter designs generally comprise an elongated tube having a balloon located at its distal end. The catheter tube includes one or more lumens, which extend longitudinally throughout essentially the entire length of the tube. At least one of the lumens is coupled at its distal end in fluid communication with the interior of the balloon such that it functions as a conduit for the flow of pressurized fluid from the proximal end of the catheter tube to the balloon.
Angioplasty dilatation balloon catheters are used to dilate and open vessels restricted by an atherosclerotic lesion or stenosis. To this end, dilatation balloon catheters include an expandable balloon, which when positioned across the restriction may be inflated with pressurized fluid such that the balloon expands and compresses the stenotic obstruction thereby widening the interior diameter of the vessel. In most cases, it is necessary to perform multiple inflations to sufficiently dilate the restricted vessel. After the dilatation procedure is completed, the balloon is deflated and the catheter is withdrawn from the patient.
Drug delivery balloon catheters are designed to administer therapeutic and/or diagnostic agents to a specific site within the patient's vasculature. Accordingly, drug delivery catheters typically include a perforated balloon which when positioned at the treatment site may be filled with pressurized fluid containing a therapeutic and/or diagnostic agent. When the balloon is sufficiently pressurized with the fluid agent, the fluid migrates through the apertures in the balloon wall and is delivered to the treatment site.
Syringe devices are commonly used by the medical profession for injecting pressurized fluid into either a dilatation balloon catheter or a drug delivery balloon catheter. In its basic form, these syringe devices typically comprise a cylinder and plunger assembly. The cylinder defines an interior chamber having an opening at its proximal end and a fluid conduit at its distal end adapted to be connected in fluid communication to a balloon catheter. The plunger includes a piston movably disposed within the chamber, wherein the piston is connected to the distal end of a shaft which extends through the opening at the proximal end of the cylinder. The plunger further includes a handle connected to the proximal end of the shaft.
In this basic configuration, pressurized fluid contained within the chamber may be forced out of the fluid conduit and into the balloon catheter by manually extending the plunger into the cylinder. Accordingly, the pressure and rate at which the fluid is injected into the balloon catheter depends on the pressure applied on the syringe plunger by the administering physician. It has been found that the precise control of the pressure and rate at which the inflation fluid is injected into the balloon catheter is important, thus requiring great skill on the part of the administering physician. For example, the exertion of excessive pressure on the syringe plunger by the physician may result in over-pressurization of the fluid within the balloon. With regard to a dilatation balloon catheter, such over-pressurization of the fluid within the balloon may cause the balloon to over-inflate to the extent that it exerts excessive pressure on the vessel wall or possibly bursts. With regard to a drug delivery balloon catheter, such over-pressurization may cause high velocity jetting of the fluid through the balloon apertures resulting in possible trauma to the treatment site.
Various syringe devices have been developed for use in catheterization procedures which enable controlled pressurization of the inflation fluid through the incremental movement of the plunger within the cylinder. One design feature commonly implemented involves providing threaded engagement between the plunger shaft and the syringe cylinder. To this end, the plunger shaft is fitted with a screw thread which engages with a complementary screw thread fitted within the opening at the proximal end of the cylinder. According to this design, the plunger may be incrementally advanced within the cylinder by rotating the handle located at the proximal end of the shaft. In addition, similar designs have included pressure gauges for measuring and displaying the pressure of the inflation fluid to the attending physician during the procedure.
Although these designs provide a syringe device which enables the administering physician to more precisely control the pressure and flow rate of the fluid injected into the catheter, they do not offer a mechanism for preventing the over-pressurization of the catheter balloon. Since the pressure and flow rate of the inflation fluid remains dependent on the administering physician, these devices are susceptible to over-pressurization of the catheter balloon through human error. Moreover, it has been found that the use of a pressure gauge to assist the physician in monitoring the pressure at which the inflation fluid is injected into the catheter does not ensure precise control of the infusion of inflation fluid to the catheter balloon. For example, a drop in the pressure indicated on the pressure gauge generally causes the physician to accelerate the movement of the syringe plunger into the syringe barrel, thereby resulting in a pressure spike. Any such pressure spike may result in over-pressurization of the balloon.
Therefore, there exists a need for an apparatus for limiting the pressure and flow rate of the inflation fluid being dispensed from the syringe device to prevent the over-pressurization of the catheter balloon.